chore: add an example named is13

.gitignore

@@ -3,3 +3,4 @@
 **/*.rs.bk
 Cargo.lock
 .deps/
+/examples/is13

README.md

@@ -40,4 +40,4 @@ You can also run the tests:
 make test
 ```
 
-CKB VM has already included RISC-V binaries used in tests, so you don't need a RISC-V compiler to build binaries. However if you do want to play with your own binaries, a RISC-V compiler might be needed. [riscv-tools](https://github.com/riscv/riscv-tools) can be a good starting point here, or if you are an expert on GNU toolchain, you might also compile upstream GCC from source with RISC-V support. CKB VM is using standard RISC-V instructions and ELF binary format, so theoretically any RISC-V compatible compilers are able to produce contracts used in CKB VM(tho bug reports are very welcome if you find breakage).
+CKB VM has already included RISC-V binaries used in tests, so you don't need a RISC-V compiler to build binaries. However if you do want to play with your own binaries, a RISC-V compiler might be needed. [riscv-tools](https://github.com/riscv/riscv-tools) can be a good starting point here, or if you are an expert on GNU toolchain, you might also compile upstream GCC from source with RISC-V support, [here](./examples/is13.rs) is an example. CKB VM is using standard RISC-V instructions and ELF binary format, so theoretically any RISC-V compatible compilers are able to produce contracts used in CKB VM(tho bug reports are very welcome if you find breakage).

examples/is13.c

@@ -0,0 +1,25 @@
+#include <string.h>
+
+int is13(char* data) {
+    if (strcmp(data, "13") == 0) {
+        return 0;
+    }
+    if (strcmp(data, "0xd") == 0) {
+        return 0;
+    }
+    if (strcmp(data, "0o15") == 0) {
+        return 0;
+    }
+    if (strcmp(data, "0b1101") == 0) {
+        return 0;
+    }
+    return 1;
+}
+
+int main(int argc, char* argv[]) {
+    if (argc == 1) {
+        return 1;
+    }
+    return is13(argv[1]);
+}
+

examples/is13.rs

@@ -0,0 +1,45 @@
+// Example "is-thirteen" is a useless(almost) program for just checking if a number is equal to 13.
+//
+// But it's also important because it shows how to compile a program from C source code and then run
+// it by ckb-vm. So, Let's start.
+//
+// To build the "is13.c" to riscv output, you will need to install "riscv-gnu-toolchain" in your system.
+//
+//   $ git clone --recursive https://github.com/riscv/riscv-gnu-toolchain
+//   $ cd riscv-gnu-toolchain
+//   $ mkdir build && cd build
+//   $ ../configure --prefix=/opt/riscv --with-arch=rv32imac --with-abi=ilp32
+//   $ make
+//
+// On my ubuntu machine, it takes 1 hours. Sad.
+//
+// Then, you can build "is13.c" by "riscv32-unknown-elf-gcc"
+//
+//   $ riscv32-unknown-elf-gcc -o is13 is13.c
+//
+// Where can you find the "riscv32-unknown-elf-gcc", depending on the previous "../configure --prefix=xxxx"
+//
+// Now, you have the "is13" binary! Copy the file to this directory, call it by ckb-vm, as shown in the Rust
+// code below. And feel free to run this example by command "cargo":
+//
+//     $ cargo run --example is13 13
+//  or $ cargo run --example is13 0xd
+//  or $ cargo run --example is13 HELLO
+use bytes::Bytes;
+use std::io::Read;
+
+fn main() {
+    let args: Vec<Bytes> = std::env::args().map(|a| a.into()).collect();
+
+    let mut file = std::fs::File::open("examples/is13").unwrap();
+    let mut buffer = Vec::new();
+    file.read_to_end(&mut buffer).unwrap();
+    let buffer = Bytes::from(buffer);
+
+    let r = ckb_vm::run::<u32, ckb_vm::SparseMemory<u32>>(&buffer, &args[..]).unwrap();
+    match r {
+        1 => println!("{:?} is not thirteen", args[1]),
+        0 => println!("{:?} is thirteen", args[1]),
+        _ => panic!(""),
+    }
+}